1. Field of the Invention
The present invention relates to a vacuum processing method using a high-frequency power, which is used for forming a deposited film, etching and so on in semiconductor devices, electrophotographic photosensitive members, image input line sensors, photographing devices, photovoltaic devices and so on.
2. Related Background Art
As for deposited film forming methods used for semiconductor devices, electrophotographic photosensitive members, image input line sensors, photographing devices, photovoltaic devices, other various electronic elements and optical elements, many methods such as a vacuum evaporation method, a sputtering method, an ion plating method, a thermal CVD method, an photo-chemical vapor deposition method and a plasma CVD method are conventionally known, and apparatuses therefor are put into practice.
Among others, the plasma CVD method, that is, a method of decomposing a material gas by a direct current or a high-frequency or a microwave glow discharge to form a thin film-like deposited film on a substrate is currently so commercialized as a suitable method for forming a hydrogenated amorphous silicon deposited film for an electrophotography and so on, and various apparatuses for the method therefor are proposed.
Here, a deposited film forming apparatus using the plasma CVD method will be described by referring to FIG. 4. FIG. 4 is a schematic block diagram showing an example of the conventional deposited film forming apparatus by a RF plasma CVD method using an RF-band frequency as a power supply, which is specifically an apparatus for forming a light-receiving member for an electrophotography.
If roughly divided, this apparatus is comprised of a deposition apparatus 2100, a material gas supplying apparatus 2200 and an exhauster (not shown) for reducing pressure in a reaction container 2101. The reaction container 2101 of the deposition apparatus 2100 has a cylindrical substrate 2112, a substrate supporter 2113 containing a substrate heater 2113a and a material gas admitting pipe 2114 installed therein, and furthermore, a high-frequency matching box 2115 is connected to a cathode electrode 2111 constituting a part of the reaction container 2101. The cathode electrode 2111 is insulated from an earth potential by an insulator 2120, and a high-frequency voltage is applicable between it and the cylindrical substrate 2112 also serving as an anode electrode maintained at the earth potential through the substrate supporting member 2113.
The material gas supplying apparatus 2200 is comprised of a plurality of gas cylinders 2221 to 2226 for accommodating material gases such as SiH4, GeH4, H2, CH4, B2H6 and PH3, gas cylinder valves 2231 to 2236, gas inflow valves 2241 to 2246, gas outflow valves 2251 to 2256 and massflow controllers 2211 to 2216, where each material gas cylinder is connected to the gas admitting pipe 2114 in the reaction container 2101 via a material gas piping 2116 having a supplementary valve 2260.
Formation of the deposited film of which main component is silicon by using the deposited film forming apparatus thus constituted is performed as follows for instance.
First, the cylindrical substrate 2112 is set in the reaction container 2101, and air is exhausted from inside the reaction container 2101 by an exhauster (a vacuum pump for instance) that is not shown. Subsequently, the substrate heater 2113a built into the substrate supporting member 2113 controls a temperature of the cylindrical substrate 2112 to be the predetermined temperature between 200xc2x0 C. and 350xc2x0 C.
To admit the material gas for forming the deposited film into the reaction container 2101, it is checked that the gas cylinder valves 2231 to 2236 and a leak valve 2117 of the reaction container 2101 are closed, and it is also checked that the gas inflow valves 2241 to 2246, gas outflow valves 2251 to 2256 and the supplementary valve 2260 are open, and then a main valve 2118 is opened first to exhaust air from inside the reaction container 2101 and the material gas piping 2116.
Next, the supplementary valve 2260 and the gas outflow valves 2251 to 2256 are closed when a vacuum gage 2119 reads approximately 7xc3x9710xe2x88x921 Pa.
Subsequently, the gas cylinder valves 2231 to 2236 are opened to let the gases in from the gas cylinders 2221 to 2226, and each gas pressure is adjusted to be 0.2 Mpa by pressure regulators 2261 to 2266.
Next, the gas inflow valves 2241 to 2246 are gradually opened to admit the gases into the massflow controllers 2211 to 2216.
After preparation for film formation is completed as above, each layer is formed by means of the following procedure.
When the cylindrical substrate 2112 reaches the predetermined temperature, necessary ones of the gas outflow valves 2251 to 2256 and the supplementary valve 2260 are gradually opened to admit predetermined gases into the reaction container 2101 from the gas cylinders 2221 to 2226 via the material gas admitting pipe 2114. Next, an adjustment is made by a predetermined massflow controller of the massflow controllers 2211 to 2216 so that each material gas will have a predetermined flow rate. At that time, openness of the main valve 2118 is adjusted by checking the vacuum gage 2119 so that the pressure in the reaction container 2101 will be a predetermined value.
When internal pressure of the reaction container 2101 becomes stable, an RF power supply of 13.56 MHz frequency (not shown) is set at a desired power, and the RF power is admitted into the reaction container 2101 through the high-frequency matching box 2115 and the cathode electrode 2111 so that the cylindrical substrate 2112 acts as an anode to generate the glow discharge. This discharge energy decomposes the material gases admitted in the reaction container 2101 to form the predetermined deposited film of which main component is silicon on the cylindrical substrate 2112.
After a desired film thickness is formed, supply of the RF power is stopped, and the gas outflow valves 2251 to 2256 are closed to stop inflow of the gases into the reaction container 2101 so as to finish formation of the deposited film. A light-receiving layer having a desired multi-layer structure can be formed by repeating the same operations a plurality of times.
It is needless to say that, when forming each layer, all the gas outflow valves 2251 to 2256 other than those for necessary gases are closed, and as required, an operation of closing the gas outflow valves 2251 to 2256 and opening the supplementary valve 2260 and further fully opening the main valve 2118 is performed to make the inside of the system a high vacuum once and exhaust air from inside the piping for the purpose of avoiding remaining of each gas in the reaction container 2101 and in the piping from the gas outflow valves 2251 to 2256 to the reaction container 2101.
Moreover, to ensure the uniform film thickness and film quality, it is effective to rotate the cylindrical substrate 2112 with a driving system (not shown) at a predetermined speed while forming a layer. Furthermore, it is needless to say that the above-mentioned gas types and valve operations are changed according to conditions for making each layer.
In addition to such conventional deposited film forming apparatuses and methods by an RF plasma CVD method using the above RF-band frequency, a VHF plasma CVD method using a high-frequency power in a VHF band (hereinafter, referred to as the xe2x80x9cVHF-PCVD methodxe2x80x9d) is receiving attention in recent years, and development of various types of deposited film formation is actively underway. This is because it is expected that, as the VHF-PCVD method allows a high speed of film deposition and acquisition of a high quality deposited film, it is possible to simultaneously accomplish lower costs and higher quality of products. For instance, Japanese Patent Application Laid-Open No. 6-287760 corresponding to U.S. Pat. No. 5,534,070 discloses the deposited film forming apparatus and method using the high-frequency power of which frequency is 30 MHz to 300 MHz, which is used to form an amorphous silicon light-receiving member for an electrophotography. In addition, development of the deposited film forming apparatus, as shown in FIG. 5A and FIG. 5B, of very high productivity capable of concurrently forming a plurality of electrophotographic light-receiving members is underway.
FIG. 5A and FIG. 5B are a diagram showing another conventional deposited film forming apparatus, where FIG. 5A is a schematic longitudinal section thereof and FIG. 5B is a schematic sectional view along its cutting line 5Bxe2x80x945B in FIG. 5A.
The apparatus shown in FIG. 5A has an exhaust pipe 311 integrally formed on a side of a reaction container 301, and the other end of the exhaust pipe 311 is connected to the exhauster that is not shown. Six cylindrical substrates 305 that have the deposited films formed on their surfaces are placed as if surrounding the center of the reaction container 301 and in parallel. Each cylindrical substrate 305 is held by a rotation axis 308 and heated by a heating element 307. If a motor 309 is driven, the rotation axis 308 rotates via a reduction gear 310 and the cylindrical substrate 305 revolves around its generatrix direction central axis.
A film forming space 306 surrounded by the six cylindrical substrates 305 has the material gases supplied from a material gas supply means 312. A VHF power is supplied to the film forming space 306 by a cathode electrode 302 from a VHF power supply 303 via a matching box 304. At this time, the cylindrical substrates 305 maintained at the earth potential through the rotation axis 308 serve as anode electrodes.
The deposited film formation using such an apparatus can be performed in outline by using the following procedure.
First, the cylindrical substrates 305 are placed in the reaction container 301, and air is exhausted from inside the reaction container 301 through the exhaust pipe 311 by an exhauster that is not shown. Subsequently, the cylindrical substrates 305 are heated and controlled by the heating element 307 at the predetermined temperature of 200 to 300xc2x0 C. or so.
When the cylindrical substrates 305 reach the predetermined temperature, the material gases are admitted into the reaction container 301 via the material gas supply means 312. After checking that the flow rate of the material gases reached a predetermined flow rate and the pressure in the reaction container 301 became stable, the predetermined VHF power is supplied to the cathode electrode 302 from a high-frequency power supply 303 via a matching box 304. Thus, the VHF power is admitted between the cathode electrode 302 and the cylindrical substrates 305 also serving as the anode electrodes, so that the glow discharge is generated in the film forming space 306 surrounded by the cylindrical substrates 305, and the material gases are dissociated by excitation to form the deposited films on the cylindrical substrates 305.
After the desired film thickness is formed, the supply of the VHF power is stopped, and the supply of the material gases is subsequently stopped so as to finish the deposited film formation. The light-receiving layer having a desired multi-layer structure for an electrophotography is formed by repeating the same operations a plurality of times.
During the deposited film formation, the deposited films are formed all over the surfaces of the cylindrical substrates by rotating the cylindrical substrates 305 at the predetermined speed by the motor 309 via the rotation axis 308.
Excellent deposited film formation, that is, vacuum processing is performed by using the above deposited film forming apparatus and the conventional method. However, the level of market requirement for such products using such vacuum processing is becoming increasingly higher, so that the vacuum processing method capable of implementing higher quality and lower costs is desired in order to meet the requirement.
For instance, in the case of an electrophotographic apparatus, improvement in a copying speed, higher image quality and lower prices are very strongly required, and in order to implement these, it is essential to improve photosensitive member characteristics that are specifically chargeability and sensitivity, control image defects arising from photosensitive member structural faults appearing as white or black points on images and reduce photosensitive member production costs. Moreover, in a digital electrophotographic apparatus and a color electrophotographic apparatus that are becoming remarkably popular in recent years, not only a written manuscript but photos, pictures and designed drawings are also frequently copied so that reduction of image density unevenness is required more strongly than before.
While optimization of deposited film lamination composition and so on are conducted aiming at improvement in such photosensitive member characteristics and reduction of the photosensitive member production costs, improvement in the aspect of the vacuum processing method is also strongly desired.
Under such circumstances, the status quo is that there is still a room left for improvement as to enhancement in vacuum processing characteristics and reduction of the vacuum processing costs in the aforementioned conventional vacuum processing method.
As already mentioned, it is possible to accomplish improvement in the vacuum processing speed and improvement in the vacuum processing characteristics by using the VHF band or the high-frequency power of the frequency in the neighborhood thereof to generate plasma and perform the vacuum processing, and earnest research is conducted for that purpose. In the case of using the high-frequency power in such a frequency band, however, a wavelength of the high-frequency power in the reaction container becomes as long as the reaction container, a high-frequency electrode, a substrate or a substrate holder, and so the high-frequency power is apt to form a standing wave in the reaction container so that this standing wave causes the power to be strong or weak at each location, thus leading to different plasma characteristics. Consequently, it was difficult to render the vacuum processing characteristics further uniform in a broad range.
As means for solving such a problem, it is thinkable to simultaneously supply a plurality of high-frequency powers of different frequencies. While a plurality of standing waves of different wavelengths according to the respective frequencies are thereby formed in the reaction container, the plurality of standing waves are synthesized since they are simultaneously supplied and no definite standing wave is formed as a consequence. Based on this idea, the frequencies of a plurality of different high-frequency powers can have the effect of curbing the standing waves irrespective of their values. For instance, Japanese Patent Application Laid-Open No. 60-160620 (corresponding to EP-0149089) discloses a plasma reactor apparatus with a configuration for supplying the high-frequency power of 10 MHz or higher and that of 1 MHz or lower to the same electrode, and Japanese Patent Application Laid-Open No. 9-321031 (corresponding to U.S. Pat. No. 5,891,252) discloses the plasma processing apparatus with a configuration for simultaneously applying the high-frequency power of a UHF band (300 MHz or higher, 1 GHz or lower) and that having the frequency different therefrom by twice or more.
It is thinkable that, by using these technologies, the standing waves of the high-frequency power in the reaction container are controlled so that uniformity of the vacuum processing will improve.
However, as a result of conducting an experiment on the uniformity of the vacuum processing characteristics by using the technology disclosed by Japanese Patent Application Laid-Open No. 60-160620, the inventors hereof could certainly improve the uniformity to a certain level but could not acquire the uniformity level that is required in recent years. In addition, as a result of conducting the experiment by using the technology disclosed by Japanese Patent Application Laid-Open No. 9-321031, the level was not acquired, either. To be more specific, it became evident that, even by using a power supply method that is rendered uniform in terms of electric field strength, non-uniformity remains to a certain extent in the actual vacuum processing.
An object of the present invention is to provide a vacuum processing method whereby an article to be processed is placed in a reaction container and at least two high-frequency powers having mutually different frequencies are simultaneously supplied to the same high-frequency electrode to have plasma generated in the above described reaction container by the high-frequency powers admitted into the above described reaction container from the high-frequency electrode so as to process the above described article to be processed, which method is characterized using as the above described high-frequency powers at least the high-frequency power of a frequency f1 and that of a frequency f2 satisfying the following two conditions:
250 MHzxe2x89xa7f1 greater than f2xe2x89xa710 MHz 
0.9xe2x89xa7f2/f1xe2x89xa70.1. 
Another object of the present invention is to provide the vacuum processing method whereby improvement in the vacuum processing speed and improvement in the vacuum processing characteristics are accomplished, and in addition, uniformity of the vacuum processing characteristics is rendered very high-level and vacuum processing costs can be reduced.